In 1920, for the first time, the Census Bureau counted more people living in urbanized America than in the countryside. This hasn’t been a rural nation ever since.

Yet the idea of Thomas Jefferson’s agrarian America has receded slowly despite demographic change. We still romanticize the family farm, though relatively few of them exist anymore. We view even suburbia in pastoral terms — the “crabgrass frontier,” as the historian Kenneth T. Jackson put it. And, as the recent Electoral College results make clear, we still live with political institutions that have baked in a distinctly pro-rural bias, by design.

The Democratic candidate for president has now won the popular vote in six of the last seven elections. But in part because the system empowers rural states, for the second time in that span, the candidate who garnered the most votes will not be president.

Rural America, even as it laments its economic weakness, retains vastly disproportionate electoral strength. Rural voters were able to nudge Donald J. Trump to power despite Hillary Clinton’s large margins in cities like New York. In a House of Representatives that structurally disadvantages Democrats because of their tight urban clustering, rural voters helped Republicans hold their cushion. In the Senate, the least populous states are now more overrepresented than ever before. And the growing unity of rural Americans as a voting bloc has converted the rural bias in national politics into a potent Republican advantage.

“If you’re talking about a political system that skews rural, that’s not as important if there isn’t a major cleavage between rural and urban voting behavior,” said Frances Lee, a professor of government and politics at the University of Maryland. “But urban and rural voting behavior is so starkly different now so that this has major political consequences for who has power.

“And it’s not just in terms of policy outcomes,” she continued. “This pervasively advantages Republicans in maintaining control of the U.S. national government.”

The Electoral College is just one example of how an increasingly urban country has inherited the political structures of a rural past. Today, states containing just 17 percent of the American population, a historic low, can theoretically elect a Senate majority, Dr. Lee said. The bias also shapes the House of Representatives.

It exists, as a result, in the formulas that determine where highway funds are spent or who gets Homeland Security dollars. It exists in state capitols, where bills preferred by urban delegations have been much more likely tobe rejected.

Today, the influence of rural voters also evokes deeply rooted ideals about who should have power in America. Jefferson and James Madison argued that the strength of the nation would always derive from its agrarian soil.

“They had this vision of what they called the ‘yeoman farmer’: this independent, free-standing person who owed nothing to anybody, who didn’t receive any payments from the government, who didn’t live by a wage, but who could support himself and his family on a farm growing everything they needed — and that these were the people who were going to be the backbone of democracy,” said Gerald Gamm, a political scientist at the University of Rochester, describing what could be the forefathers of the rural voters who tilted this year’s election.

When the framers of the Constitution were still debating the shape of institutions we have today, 95 percent of America was rural, as the 1790 census classified the population. The Connecticut Compromise at the time created the Senate: one chamber granting equal voice to every state to counterbalance the House, where more populous states spoke louder.

And they made sure the compromise stuck. Today, equal state representation in the Senate is the only provision in the Constitution that remains singled out for protection from the amendment process; no state can lose its full complement of senators without its permission.

But even as a deliberately undemocratic body, the Senate has slipped further out of alignment with the American population over time.

“When we talk about small-state bias, all of that was an intentional policy choice,” said Jowei Chen, a political scientist at the University of Michigan. Republicans in Congress passed the 1862 Homestead Act, offering free land to settlers who would move to territories that would eventually become states — creating more Senate seats and Electoral College votes for a Republican Party eager to keep government control away from Southern Democrats. They even managed to divide the Dakota Territory into two states, worth twice the political power.

As the Plains later depopulated and American cities, then suburbs, swelled, the Senate became even more unrepresentative.

Jeffersonian suspicion of big cities also appears in the sites of state capitals: Albany and not New York; Jefferson City and not St. Louis; Springfield and not Chicago. Political scientists at the University of California, Davis, have found that most state capitals were located near what was then the population centroid of each state — typically closer to the geographical center of the state, and not the place where the most people already lived, breaking with how much of the world sited its capitals.

The state legislatures there also grew significantly less representative as America urbanized. In 1961, when lawyers in Tennessee brought what would be a seminal case before the Supreme Court challenging the practice, the state legislature had not reapportioned its districts to reflect population change in 60 years. Maryland was still using districts drawn in 1867.

Even states that had constitutions requiring equal population districts were ignoring them. Florida, Georgia and New Mexico gave small counties 100 times the voting power of the most populous ones. Decades ago in California, Amador County (population 14,294) had the same representation in the state’s Senate as Los Angeles County (with a population over six million).

“They justified it because that was a cultural norm; it was just the way things were,” said Stephen Ansolabehere, a Harvard professor of government. Rural legislators had no incentive to change a system that favored them. “They just let it keep getting worse. You’re in power. Why change?”

By the mid-20th century, no state approximated majority rule. America at the time, Dr. Ansolabehere and James M. Snyder Jr. wrote in their book “The End of Inequality,” had some of the most unequal representation in the world. A series of Supreme Court cases beginning with that Tennessee complaint upended this system and established the standard that equal representation means “one person, one vote.” Not one town, one vote. Or one county, one senator. Only the United States Senate, protected by the Constitution, remained unchanged.

Still, the House retains a rural bias. Republican voters are more efficiently distributed across the country than Democrats, who are concentrated in cities. That means that even when Democrats win 50 percent of voters nationwide, they invariably hold fewer than 50 percent of House seats, regardless of partisan gerrymandering.

The Electoral College then allocates votes according to a state’s congressional delegation: Wyoming (with one House representative and two senators) gets three votes; California (53 representatives and two senators) gets 55. Those two senators effectively give Wyoming three times more power in the Electoral College than its population would suggest. Apply the same math to California and it would have 159 Electoral College votes. And the entire state of Wyoming already has fewer residents than the average California congressional district.

In Washington, these imbalances directly influence who gets what, through small-state minimums (no state can receive below a certain share of education funding) and through formulas that privilege rural states (early road spending was doled out in part by land area and not road use).

There are policy reasons that the country might want to disproportionately spend resources on places with few people. Repairing an interstate highway in rural Oklahoma keeps national commerce flowing. And when the private market won’t build essential infrastructure, public investments like the New Deal’s rural electrification help fight poverty.

But even when you control for policy need, Dr. Lee’s research has found that a significant rural bias in resources persists. You can see it in Homeland Security funding that gave Wyoming, for example, seven times as much money per capita as New York after the Sept. 11 terrorist attacks. You can see it in Alaska’s proposed “bridge to nowhere.”

“In that case,” Dr. Ansolabehere said, “Alaska has so much disproportionate power in the negotiation over funds that in order for California to get some, Alaska gets a lot — to the point of not knowing what to spend the money on.”

These calculations also mean that populous states subsidize less populous ones, which receive more resources than the tax dollars they send to Washington.

The challenge for rural voters now is that their electoral strength, and even these funding formulas, have not translated into policies that have fixed the deep economic problems they face, from high unemployment to declining wages. And it’s unclear how Mr. Trump will do that for them, either — even if his major infrastructure proposal comes to pass and helps rebuild their roads.

If he can’t, rural voters may stray from his party again. In that future, the rural bias in American politics would persist. But Democrats might yet have a chance to blunt its effects.

Correction:

An Upshot article on Monday about the disproportionate voting power of rural states referred incorrectly to the Constitution’s provision for equal state representation in the Senate, the only provision that remains singled out for protection from the amendment process. The provision may be amended, but only with the consent of any state whose representation would be reduced. It is not impossible for the provision to be amended.

A version of this article appears in print on , on Page A11 of the New York edition with the headline: As American as Apple Pie? The Rural Vote’s Disproportionate Slice of Power. Order Reprints | Today’s Paper | Subscribe